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Maize inflorescence development

XTwo types of inflorescences are found in maize, the tassel and the ear. The tassel forms directly from the shoot apical meristem after production of a defined number of leaves, whereas ears form at the tip of compact axillary branches. Although the mature tassel and ear are very different in appearance, their underlying organization is similar.
XA rich collection of mutants has demonstrated that distinct genetic steps can be defined in the progression from inflorescence to floral meristem in maize. These steps, the production of long branch, spikelet pair and spikelet meristems, differentiate maize from other model organisms such as Arabidopsis, and unite maize with other grasses. Our focus is primarily mutations that affect these meristems, thus producing an architectural change. The phenotypes produced by these mutants mimic some of the natural variation in the grasses.
XFor more details on our research with inflorescence mutants look at the Related Manuscripts. Here's a poster summarizing recent developments in maize mutants.
XGo to Maize GDB to enter the project portal where inflorescence data can be accessed.

Maize flowers are organized in spikelets as are all members of the grass family. Two florets are found in the spikelet. This drawing, courtesy of Bruce Veit, is of a spikelet in the tassel. Normal tassels have long branches at their base and spikelets at the top. Scanning electron microscopy shows the developing spikelet meristems on the tassel. (photo courtesy of George Chuck)
td tassel file
A thick tassel dwarf1 mutant tassel is shown on the left with a normal tassel on the right.
link to large image Notice the increased spikelet density in the middle of the tassel rachis.
td stamens
An open td1 spikelet shows additional stamens.
link to large image Single spikelets are common and occasionally, glume number is also affected in the mutant.
ears
Uncontrolled proliferation of the ear inflorescence leads to fasciation and abnormal kernel rowing. Top, td1 mutant has some reverse germ orientation and a fasciated ear tip. (Ears were open-pollinated and do not reflect a difference in fertility.)

ramosa2 mutants have spikelet pair meristems with increased indeterminacy. As a result, ears are often branched at the base and the rows are disorganized
An SEM of a ra2 ear showing branches at the base
Tassels of ra2 have upright branches, some of which bear multiple single spikelets instead of spikelet pairs
ra2 is expressed in the anlagen of axillary meristems in developing inflorescences

branched silkless 1 (bd1) mutants (left) show inflorescence branch proliferation.
A wild type ear is on the right
SEM of bd1 mutant ear showing that the spikelet meristem becomes branch-like		 Longitudinal (left) and whole mount (right) sections showing in situ hibridization of bd1.
Transcript expression is seen at the base of the spikelet meristem.

Related Manuscripts:

Bortiri, E., Chuck, G., Vollbrecht, E., Rocheford, T., Martienssen, T., and Hake, S. (2006). ramosa2 encodes a LATERAL ORGAN BOUNDARY domain protein that determines the fate of stem cells in branch meristems of maize. The Plant Cell. Online [Abstract][PDF]

Kozaki, A., Hake, S., and Colasanti, J. (2004). The maize ID1 flowering time regulator is a zinc finger protein with novel DNA binding properties. Nucleic Acids Research 32:1710-1720.

Hake, S. and Rocheford, T. (2004) Exploiting quantitative trait loci in gene discovery. Genes and Development 18:597-601.

Magnani E., Sjolander K., Hake S. (2004) From endonucleases to transcription factors: evolution of the AP2 DNA binding domain in plants. Plant Cell 16:2265-77.

Laudencia-Chingcuanco, D. and Hake, S. (2002) The indeterminate floral apex1 gene regulates meristem determinacy and identity in the maize inflorescence. Development. 129:2629-2638.

Hubbard, L. McSteen, P. Doebley, J. and Hake, S. (2002) Expression patterns and mutant phenotypes of teosinte brached1 correlate with growth suppression in maize and teosinte Genetics 162:1927-1935

Chuck G, Muszynski M, Kellogg E, Hake S, Schmidt RJ. (2002) The control of spikelet meristem identity by the branched silkless1 gene in maize. Science. 298:1238-41.

Taguchi Shiobara, F., Yuan, Z. Hake, S. and Jackson, D. (2001) The fasciated ear2 gene encodes a leucine rich repeat receptor like protein that regulates shoot meristem proliferation in maize. Genes and Development 15:2755-2766.

McSteen, P. and Hake, S. (2001) barren inflorescence2 regulates axillary meristem development in the maize inflorescence. Development 128:2881-2891.

Veit, B., Briggs, S., Schmidt, R. J., Yanofsky, M. F., and Hake, S. (1998) Regulation of leaf initiation by the terminal ear1 gene of maize. Nature 393: 166-168.

Chuck, G. Meeley, R. B. and Hake, S. (1998) The control of maize spikelet meristem fate by the APETELA2-like gene indeterminate spikelet1. Genes and Development 12:1145-1154.

McSteen, P. and Hake, S. (1998) Genetic control of plant development. Current Opinion in Biotechnology 9:189-195.

Veit, B. Schmidt, R.J., Hake, S. & Yanofsky, M.F. 1993. Maize floral development - new genes and old mutants. Plant Cell 5: 1205-1215.

Schmidt, R.J., Veit, B., Mandel, M.A., Mena, M., Hake, S. & Yanofsky, Y. 1993. Identification and molecular characterization of ZAG1, the maize homolog of the Arabidopsis floral homeotic gene AGAMOUS. 1993. Plant Cell 5:729-737.

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